1. Field of the Invention
The present invention relates to an on-line, forum-type electronic conference systems in which a plurality of users post and read messages to hold debates, conferences, discussions, talks, opinion exchanges, trivial conversations, etc.
2. Description of the Related Art
Posted messages in on-line, forum-type electronic conference systems are organized into parent-child relationships so as to allow users to have better understanding of developments in a conversation. When a comment is given in response to a particular message, this particular message is treated as a parent, and a comment message is recorded as a child. A plurality of comments can be associated with one message, and a discussion is represented by a tree structure. A first message which initiated the discussion is called a topic message (or a topic), and comment message posted in response to other messages are referred to as reply messages.
Such an electronic conference system of a small size can be built on a small network based on a single server and several clients. When a large-scale such electronic conference system needs to be constructed to service users all over the world, for example, use of a single server is not appropriate. The load on the server and the network in this case undermines efficiency. Instead of use of a single server, an electronic conference system of a large scale is usually comprised of a plurality of small electronic conference systems connected with each other. Each of these small electronic conference systems is made up from a single server and a plurality of clients, and the servers of these systems share common data.
In a distributed system such as described above, a measure has been taken to reduce the load on the network. That is, when a message is posted to a given server, this message is not promptly transferred to other servers. Instead, this message is put together with other messages which are posted within a certain timeframe, and a set of messages is periodically sent to other servers.
The same applies in the case where a message is deleted from a server. The deletion of the message is not promptly reported to other servers, but is sent along with other messages when it is time to send these messages.
In a distributed electronic conference system, older messages are not always received ahead of newer messages. An order of message arrival is dependent on ways of running the network and network structures between servers.
Transferred messages are stored in a storage, which is referred to as a folder or a conference room, for example. This storage is dynamically created and deleted as such a need arises. In some cases, however, a message to be posted is received ahead of a notice requesting a creation of the storage.
For the sake of user convenience, such electronic conference systems typically store user history information, which records access history of each user as to which messages a given user has already read. When a user requests a list of posted messages, the user history information is used for helping the user to know which messages in the list have been already read. By looking through this list of messages, the user can learn whether any new messages are added to the list.
Since such an electronic conference system has only a limited size of memory storage, old messages need to be deleted as such deletion becomes necessary in order to secure the memory area for storing new messages.
There are other cases in which messages are deleted, as in a case in which a user requests for a deletion. When a given message is deleted, comment messages associated with this given message will become a topic message.
If an attempt is made to post a reply message (a message to become a child) when a parent message is no longer in existent because of deletion, this reply message is discarded. When a reply message and a parent message are transferred from different servers, it is possible that a server of the transfer destination receives the reply message ahead of the parent message. In this case, the reply message (a message to become a child) ends up being discarded since the parent message has not yet been received. This creates a problem in that some servers have some messages while different servers have different messages.
Further, user history information which is overgrown puts pressure on the memory area of the system, giving rise to a problem that no new messages can be posted.
In order to know whether any new messages are posted, users have no choice but to display a list of the posted messages. The load is imposed on the electronic conference system when the system has to check, one message, by one message whether messages on the list have already been read by a user. Further, it is a waste of time for a user to go to the extent of displaying the whole list just for the sake of checking if there is a newly posted message.
Further, when a discussion is ongoing for a long time, messages posted at an early stage of discussion may be deleted to secure the memory area of the electronic conference system. When this happens, users who have started participating halfway through the discussion may not know what initiated the discussion and what kind of comments have been posted.
Moreover, deletion of old messages results in a single tree structure of a discussion being divided into a plurality of tree structures when a deleted message has associated comment messages (child messages). In this case, the discussion can only be represented by a plurality of tree structures, so that users participating halfway through may encounter difficulties in grasping the whole picture of the discussion.